1. Field of the Invention
The present invention relates to a mold, an imprint method, and a method of manufacturing an article.
2. Description of the Related Art
Imprint techniques make it possible to transfer nanoscale fine patterns, and are coming into practical use as one of nanolithography techniques intended for mass production of magnetic storage media and semiconductor devices. The imprint techniques employ an apparatus such as an electron-beam exposure apparatus to form a fine pattern on a substrate such as a silicon substrate or a glass plate using a mold having a fine pattern formed on it as an original. This fine pattern is formed by coating (dispensing) a resin on the substrate, and curing the resin while the pattern of the mold is pressed against the substrate via the resin. Imprint techniques that have been put into practical use at present include the heat cycle method and the photo-curing method.
In the heat cycle method, a pattern is formed by heating a thermoplastic resin to a temperature equal to or higher than a glass transition temperature, pressing the mold against the substrate via the resin with improved flow properties, cooling the mold, and separating the mold from the resin. In the photo-curing method, a pattern is formed by irradiating an ultraviolet-curing resin with ultraviolet rays while the mold is pressed against the substrate via the resin to cure the resin, and separating the mold from the cured resin. The heat cycle method suffers from prolonging the transfer time by temperature control and degradation in dimensional accuracy due to a change in temperature, whereas the photo-curing method poses no such problem. Therefore, at present, the photo-curing method is more advantageous in mass production of nanoscale semiconductor devices.
Until today, a variety of imprint apparatuses have been realized in accordance with the resin curing methods and the purposes. Assuming an apparatus intended for mass production of, for example, semiconductor devices, an imprint apparatus which exploits step-and-flash imprint lithography (SFIL) is effective. Japanese Patent Laid-Open No. 2008-509825 discloses an imprint apparatus compatible with SFIL. Such an imprint apparatus includes a substrate stage, resin coating mechanism, imprint head, light irradiation system, and positioning mark detection mechanism. The imprint apparatus as described above adopts the so-called dye-by-dye scheme in measurement for aligning the substrate and the mold. In the dye-by-dye scheme, mold-side marks and substrate-side marks are optically simultaneously observed for each shot region upon pressing the mold against the substrate, the amount of shift is corrected, and the resin is cured.
In the dye-by-dye scheme, the mold-side marks are filled with a resin upon an imprint process. Since quartz used to form the mold has nearly the same refractive index as the resin, a sufficient contract cannot be obtained in detection when the mold is filled with the resin. Hence, Japanese Patent Laid-Open No. 2008-509825 devises a measure to prevent the mold-side marks from being filled with the resin even upon an imprint process.
Even when the mold and the substrate are pressed against each other upon bringing them into tight contact with each other in an imprint process, a very small gap remains between them. The resin enters this gap, so not only a pattern but also a resin thin film is formed on the entire surface of the substrate having undergone an imprint process, regardless of the presence/absence of the pattern. This thin film is sometimes called a residual film. However, as described in Japanese Patent Laid-Open No. 2008-509825, in a structure having mark portions which are not filled with a resin, no resin thin film is formed in the mark portions, so a difference in etched state occurs between the actual element pattern portion and the mark portions upon, for example, an etching step after an imprint process.